1. Field of the Invention
The present invention concerns an apparatus for handling layers of palletized goods.
2. Description of the Prior Art
In order to make effective inexpesnive and simplified distribution of goods, most goods are sold on pallets, preferably the so-called EU pallets (800×1200 mm). A widespread need has appeared for also dispatching orders comprising lesser amounts of goods in a correspondingly effective way. Statistically it appears that many orders for small shops actually are consignments of goods which most often consist of very few layers or maybe just a single layer of palletized goods.
U.S. Pat. Nos. 3,406,938 and 3,229,953 describe a lifting device and an item holder using relatively complicated lifting or holding faces which have a large number of lesser chambers that are open toward the lifting face and the holding face, respectively. For lifting or holding of, by way of example, plate shaped items with different outer shapes or sizes in the printing industry, it is known to use lifting or holding faces with a differentiated vacuum chamber system, having a number of uniform, but individually connected chambers. These chambers by means of a valve system may be connected with one or more vacuum sources in such a way that sheets or plates with individual shape or size may be lifted or held fast with one and the same lifting or holding face.
WO-97/45355-A1 discloses an apparatus for lifting and moving of articles, comprising at least one arrangement with a cavity, hereafter called vacuum chamber, which is connected to an arrangement which is capable of producing negative pressure in the vacuum chamber. The underside of the lower plate is provided with an elastic airtight bottom and also is provided with a number of first through-passages to the vacuum chamber. With the invention each first passage is of a cylindrical design with a diameter reduction in the part which is connected to the vacuum chamber, forming a shoulder in the passage. The passage contains a body arranged moveably in the passage. In the body are planes which are at right angles to the center line of the passage which has a greatest diameter which is only slightly smaller than the diameter of the first passage. The first passage is provided with a second passage with a considerably smaller diameter than the first passage. The body is capable of essentially blocking the first passage when a negative pressure is obtained in the vacuum chamber with the exception of a given air flow in the second passage.
WO-00/64790-A1 and corresponding U.S. Pat. No. 6,802,688 discloses an apparatus for handling layers of palletized goods. The apparatus comprises a vertically displaceable lift head with a horizontal suction face which in size is adapted to a pallet and has a large number of downwardly opening suction chambers. The suction face is arranged to be moved downwards against the top side of an upper layer of individually or groupwise packed goods on a pallet. The suction chambers via individual valves are connected with a source of vacuum incorporated in the lift head, where the apparatus is intended for interacting with a depalletizing system. The valves between the suction chambers and the source of vacuum are designed as ball valves with very light thin-walled valve bodies that are enclosed in the suction chamber by means of lateral projections or by means of a retainer net, and which interact with upper round valve openings with spherical valve seats at the bottom if the actual suction chamber is not blocked at the bottom by contacting the top side of the goods in an upper pallet layer. Along the outer sides of the suction face, the lift head comprises means for exerting an inwardly pressure at the outer sides of the goods in the uppermost pallet layer. The description of the this invention is incorporated in the present application by reference.